A fuel injector is commonly used to deliver fuel to a combustion chamber in an internal combustion engine. The fuel injector may deliver a certain quantity of fuel, which may be, for example, diesel, gasoline, or natural gas, to the combustion chambers in the engine at a certain time in the operating cycle of the engine. The amount of fuel delivered to the combustion chamber may depend on the operating conditions of the engine such as, for example, the engine speed and the engine load.
Precisely controlling the quantity and timing of the fuel delivered to each combustion chamber in the engine may lead to an increase in engine efficiency and/or a reduction in the generation of undesirable emissions. To improve control over the quantity and timing of fuel delivery, a typical fuel injection system includes an electronic control module that controls each fuel injector. The electronic control module transmits a control signal to each fuel injector in the engine to deliver a certain quantity of fuel to the combustion chamber at a certain point in the operating cycle.
However, due to manufacturing and/or assembly variations, each individual fuel injector may respond differently to an identical control signal. The different response characteristics of the individual fuel injectors may lead to fuel injectors that receive the same control signal delivering a different quantity of fuel to the combustion chamber. In addition, the different response characteristics of the individual fuel injectors may result in each fuel injector having a different delay period between the application of the control signal and the start of fuel injection.
An engine may experience performance problems if the amount and/or timing of fuel delivered to each combustion chamber diverges from an acceptable tolerance range. For example, the engine may generate an unequal amount of torque when the amount of fuel delivered to one combustion chamber is greater than the amount of fuel delivered to another combustion chamber in the engine. The unequal torque may result in an increased fatigue in engine and/or vehicle components, thereby increasing the amount of maintenance required to keep the vehicle operational.
Several different approaches may be followed to account for the variability in fuel injector operation. For example, the engine may be “over-designed” to compensate for the fuel injector variability. In this approach, the engine is designed with the realization that the engine will experience a decrease in efficiency due to fuel injector variability. The engine is designed such that the theoretical maximum output is greater than the desired output. In operation, the output of the engine will be reduced by the fuel injector variability, but the engine will still generate the desired output.
Alternatively, the manufacturing tolerances for the fuel injectors and fuel injector components may be tightened to reduce the variability between fuel injectors. This tightening of the manufacturing tolerances may reduce the performance variability between fuel injectors. However, the tightening of the manufacturing tolerances will increase the cost associated with manufacturing each fuel injector.
In yet another approach, each fuel injector may be tested to determine the performance characteristics of the particular fuel injector. The fuel injectors may then be grouped into matched sets of fuel injectors that have similar performance characteristics. A matched set of fuel injectors may then be installed on an engine. In this manner, the variability between fuel injectors on an engine may be reduced. However, this approach increases the complexity of the assembly process of the fuel injectors as the injectors must be sorted into many different groups. In addition, this approach increases the complexity of the maintenance process for the engine, particularly when a fuel injector must be replaced or repaired.
In still another approach, the control signal sent to each fuel injector by the electronic control module may be modified to account for the performance characteristics of the particular fuel injector. As described in U.S. Pat. No. 5,634,448 to Shinogle et al., the performance of each fuel injector may be tested in response to a large number of control signals and at number of different operating conditions. Based on this testing, a calibration, or adjustment, parameter may be established for each fuel injector. This adjustment parameter may be used by the engine control module to modify the control signal sent to the fuel injector. Thus, the engine control module may transmit different control signals to each fuel injector to achieve a consistent amount and timing of fuel delivery.
However, the calibration process described in U.S. Pat. No. 5,634,448 requires testing of each fuel injector to determine the appropriate adjustment parameter. In the described process, each fuel injector is tested at a plurality of operating conditions to identify the appropriate performance characteristics. This extensive testing may be a time consuming process that increases the cost of the fuel injectors.
The method and apparatus of the present disclosure solves one or more of the problems set forth above.